Ethanol is a renewable, environmentally friendly fuel that is inherently cleaner than gasoline. While all feedstocks for ethanol compare favorably to petroleum, the degree of the environmental advantage depends on the feedstock in question.

Source: Renewable Fuels Association

Better for the Air:

The Carbon Cycle

• Unlike the production process for petroleum, the ethanol production process represents a carbon cycle.
  
• Thus, the feedstocks used to produce ethanol absorb carbon dioxide (C02) during growth, “recycling” the carbon that is released during fuel combustion.
• In addition, many ethanol plants collect that carbon dioxide released during fuel combustion and market it as co-product.

Ethanol reduces greenhouse gas (GHG) emissions. 

• Petroleum-based transportation fuels are the number one cause of air pollution in the U.S. The U.S. Department of Energy estimates that 82 percent of the carbon monoxide, 43 percent of the reactive organic gases (precursors to ground level ozone) and 57 percent of the nitrogen oxides in U.S cities are emitted from petroleum fuels.
• In 2006, ethanol use in the U.S. reduced C02-equivalent greenhouse gas emissions by approximately 7.8 million tons, equal to removing the annual emissions of more than 1.18 million cars from the road (Argonne National Laboratory (ANL) GREET Model)
• Ethanol blends are estimated to reduce carbon monoxide emissions in vehicles by between 10% - 30%, depending upon the combustion technology, thereby reducing smog and ozone forming tailpipe emissions. (Environmental Protection Agency - EPA)
• The American Lung Association of Metropolitan Chicago credits ethanol-blended fuel with reducing smog-forming emissions by 25% since 1990.
• Cellulosic ethanol use could reduce GHGs by as much as 100%. (U.S. Department of Energy)

"Ethanol Life-Cycle Effect on GHG"

Source: IMF World Energy Outlook, 2007

 (Graph by George Philippidis of Florida International University)

Ethanol is an oxygenate. 

• The 1990 Clean Air Act Amendments require that motor vehicles add oxygenates to fuels. Adding oxygen to gasoline allows for more complete combustion of the fuel, which reduces exhaust emissions of CO (carbon monoxide), which can result in lower levels of toxic, ozone-forming pollutants and greenhouse gases. (State Energy Conservation Office of Texas - SECO)
• Traditionally, MTBE (methyl tertiary-butyl ether), a chemical compound that is manufactured by the chemical reaction of methanol and isobutylene, has been used as an oxygenate for gasoline.
• However, studies have shown that MTBE pollutes groundwater and is a possible carcinogen.

• Ethanol has widely replaced MTBE because: (SECO)

                   • Adding oxygen to gasoline allows for more complete combustion of the fuel, which reduces exhaust emissions of CO

                     (carbon monoxide), which can result in lower levels of toxic, ozone-forming pollutants and greenhouse gases,

                     especially if higher-level ethanol blends are used.

                   • Ethanol has the advantages of MTBE without the same dangers, and it contains 35 percent oxygen by weight,    

                     twice the oxygen content of MTBE. Ethanol is the highest-octane fuel in the market. Because it doesn't leave

                    gummy deposits, it helps to keep the vehicle's fuel system clean for optimal performance.

                   • Ethanol extends gasoline supplies.

• Ethanol is nontoxic and biodegradable in nearly all environments and thus is an excellent alternative to MTBE — a fuel oxygenate derived from petroleum — which is banned in many states because it has been shown to contaminate groundwater.
• Ethanol spillage is virtually harmless to the environment, eliminating the many adverse effects associated with oil spills.